Many industries use robotics to speed up manufacturing, improve product quality, reduce costs, and provide a safer working environment for employees. Rigid parts can be roboticly worked by securing them to a work station so that the part is located at specific coordinates. The robot is then programmed to move along a predetermined path of travel, and to rotate, twist and turn at prescribed points along that path so that the robot performs the same tasks at the same places on each part passing through the work station. Such robotic work stations process parts quickly and manufacture them to relatively high degree of tolerances.
Problems arise with robotics when the parts being produced are made of a flexible material. Robotic machines do not readily take into consideration the variables associated with flexible parts. Flexible parts bend and vibrate when the tool engages them, which results in imprecision and flaws in the finished product. Although attempts have been made to program robots with feedback loops to accommodate for the variables associated with flexible parts, to date, such attempts have proved commercially unsuccessful in many manufacturing applications. For example, robots used to cut and trim the edges of flexible hot molded plastic sheets either perform too slowly or the edges of the parts are cut and trimmed inconsistently.
Additional problems arise when flexible parts are secured against a rigid surface or fixture prior to engaging the robotic tool. The flexible parts tend to take the shape of the surface of the fixture, including any imperfection in the shape of the fixture. These imperfections are then passed on to the finished part. This problem is compounded if the fixture is subject to harsh treatment do to its close proximity to the robotic tool. The fixture may need to be frequently replaced if struck by the robot or tool. This can dramatically increase the cost of the manufacturing process and the finished product. Yet, fixtures made of inexpensive components tend to have significant imperfections in their shape. For example, low cost iron and aluminum beams frequently have significant warping along the length of the beam.
A still further problem is that the stiffness or flexibility of the parts being manufactured may differ from part to part. For example, a sheet of hot molded plastic has different flexibility characteristics depending on the thickness of the sheet and how long it has been cooling since it was molded. Variations in sheet thickness as well as slow downs and shut downs in a work station can cause substantial changes in the stiffness of the plastic sheet. In some situations, the robotic arm may not be capable of supplying a sufficient force to push the flexible part against the fixture. This can result in inconsistencies in the parts because they are located at different coordinates during manufacture.
A still further problem arises when a part is mounted on a moving work station. This situation is common when a manufacturing process is done in an enclosed work station away from employees. The part is placed on a fixture mounted on a chassis and guide track and moved into an enclosed environment where work is performed. This adds to the difficulty in ensuring that the part is located at specific coordinates when work is performed by the robot. The fixture and chassis track may not move to exactly the same position on the guide track each time due to the design tolerances of the guide track, or due to dirt or other debris landing on the guide track. Variations in the location of the fixture are then passed on to the roboticly manufactured part.
A still further problem with robotics occurs when a part has a non-linear shape. For example, a plastic liner for a truck bed will frequently have tabs and recesses cut into its outer edge that secure the liner to the truck. The cutting and trimming tool cannot travel in a single linear path down the length of the liner when forming the tabs and recesses in the edge of the liner. Instead, the robotic arm is programmed to move from one linear path to another and back again. Each change in path of the robotic arm can cause imprecision in the finished part due to the tolerances associated with the movements of the robotic arm.
A still further problem arises in designing a robotic end effector that can automatically receive and release different tools during a manufacturing process. For example, to minimize the number of work stations needed to manufacture a product such as a plastic truck bed liner, a single robot may need to pick up, work with and put down different cutting, trimming and drilling tools. Otherwise, the product price will have to include the cost of several work stations.
A still further problem arises in designing a robotic end effector adapted for use in manufacturing a variety of differently shaped parts. As assembly lines are frequently intended to accommodate slight variations in part shape, the end effector must likewise be capable of adapting to these changes in part shape.
A still further problem arises in designing a robotic end effector that is easily adaptable for use on an existing robotic arm. The fewer modifications to the robotic arm that are necessary, the less costly and more easily the end effector will be incorporated into existing robot designs.
The present invention is provided to solve these and other problems.